Fabrication of integrated circuits (IC) on semiconductor substrates involves deposition and etching of multiple layers of materials in order to form a desired pattern of conductive paths in a layer of dielectric. Anisotropic etching (i.e. predominant etching in a selected direction) is a valuable tool for forming recessed features on semiconductor substrates. In a typical example of anisotropic etching, the material is etched out in a vertical direction, without horizontal etching. For example, the material can be removed from the bottom of a recessed feature, while preserving the width of the recessed feature.
Tungsten and tungsten-containing materials emerge as materials that find many uses in IC fabrication, both as conductive layers, and more recently as hardmasks in dynamic random-access memory (DRAM) and 3D NAND fabrication. While there is a variety of methods that can be used for tungsten deposition, including chemical vapor deposition (CVD), atomic layer deposition (ALD), and physical vapor deposition (PVD), the methods for tungsten etching are still limited. Specifically, the methods for anisotropic tungsten etching, particularly for selective anisotropic tungsten etching in a presence of dielectric materials, such as silicon oxide and silicon nitride, are in need of development.